Is Butter Back? A Systematic Review and Meta-Analysis of Butter Consumption and Risk of Cardiovascular Disease, Diabetes, and Total Mortality

Abstract

Background: Dietary guidelines recommend avoiding foods high in saturated fat. Yet, emerging evidence suggests cardiometabolic benefits of dairy products and dairy fat. Evidence on the role of butter, with high saturated dairy fat content, for total mortality, cardiovascular disease, and type 2 diabetes remains unclear. We aimed to systematically review and meta-analyze the association of butter consumption with all-cause mortality, cardiovascular disease, and diabetes in general populations.

Methods and findings: We searched 9 databases from inception to May 2015 without restriction on setting, or language, using keywords related to butter consumption and cardiometabolic outcomes. Prospective cohorts or randomized clinical trials providing estimates of effects of butter intake on mortality, cardiovascular disease including coronary heart disease and stroke, or diabetes in adult populations were included. One investigator screened titles and abstracts; and two reviewed full-text articles independently in duplicate, and extracted study and participant characteristics, exposure and outcome definitions and assessment methods, analysis methods, and adjusted effects and associated uncertainty, all independently in duplicate. Study quality was evaluated by a modified Newcastle-Ottawa score. Random and fixed effects meta-analysis pooled findings, with heterogeneity assessed using the I2 statistic and publication bias by Egger's test and visual inspection of funnel plots. We identified 9 publications including 15 country-specific cohorts, together reporting on 636,151 unique participants with 6.5 million person-years of follow-up and including 28,271 total deaths, 9,783 cases of incident cardiovascular disease, and 23,954 cases of incident diabetes. No RCTs were identified. Butter consumption was weakly associated with all-cause mortality (N = 9 country-specific cohorts; per 14g(1 tablespoon)/day: RR = 1.01, 95%CI = 1.00, 1.03, P = 0.045); was not significantly associated with any cardiovascular disease (N = 4; RR = 1.00, 95%CI = 0.98, 1.02; P = 0.704), coronary heart disease (N = 3; RR = 0.99, 95%CI = 0.96, 1.03; P = 0.537), or stroke (N = 3; RR = 1.01, 95%CI = 0.98, 1.03; P = 0.737), and was inversely associated with incidence of diabetes (N = 11; RR = 0.96, 95%CI = 0.93, 0.99; P = 0.021). We did not identify evidence for heterogeneity nor publication bias.

Conclusions: This systematic review and meta-analysis suggests relatively small or neutral overall associations of butter with mortality, CVD, and diabetes. These findings do not support a need for major emphasis in dietary guidelines on either increasing or decreasing butter consumption, in comparison to other better established dietary priorities; while also highlighting the need for additional investigation of health and metabolic effects of butter and dairy fat.

Fig 1. Flowchart of study identification and selection process.

All systematic review and meta-analyses methods conducted according to PRISMA guidelines.

Fig 2. Butter consumption and risk of all-cause mortality.

Within-study dose-response RRs were derived from reported linear effects or generalized least-squares trend estimation for studies reporting categories of intake, and pooled using both inverse-variance weighted random and fixed effects meta-analysis.

Fig 3. Butter consumption and risk of any and total cardiovascular disease, stroke only and CHD only.

Data from 4 prospective cohorts with 175,612 participants and 9,783 cases for CVD, 3 cohorts of 173,853 participants and 5,299 events for stroke, and 3 studies of 149,056 participants and 4,484 cases of CHD. Within-study dose-response RRs were derived from reported linear effects or generalized least-squares trend estimation for studies reporting categories of intake, a pooled using both inverse-variance weighted random and fixed effects meta-analysis. CHD: Coronary Heart Disease; CVD: Cardiovascular Disease; D+L: DerSimonian and Laird random effects; I-V: Inverse-variance fixed effects; RR (95%CI): Relative Risk and 95% Confidence Interval.

Fig 4. Butter consumption and risk of type 2 diabetes.

Within-study dose-response RRs were derived from reported linear effects or generalized least-squares trend estimation for studies reporting categories of intake, a pooled using both inverse-variance weighted random and fixed effects meta-analysis. D+L: DerSimonian and Laird random effects; EPIC: European Prospective Investigation into Cancer and Nutrition; I-V: Inverse-variance fixed effects; RR (95%CI): Relative Risk and 95% Confidence Interval.